Method for producing member for molten metal bath having coating film excellent in resistance to corrosion by molten metal

ABSTRACT

In a method for manufacturing a member for use in a molten metal bath, a sealing solution is applied on a coating formed of oxide system ceramics formed on an outermost surface of a substrate. The sealing solution includes an inorganic colloid compound solution containing an inorganic colloid having a grain diameter in a range of 5-50 nanometers in an amount of 5-50 weight percent, and an inorganic binder. The inorganic binder is mixed at a weight ratio of 0.3-3.0 with respect to a weight of 1.0 of the inorganic colloid. The oxide system ceramic formed on the outermost surface of the substrate is an oxide containing 5% or more of a composite oxide comprising (a) at least one of Al, Ti, V, Cr, Fe, Co, Rh, In and rare earths, which are trivalent metal elements, and (b) at least one rare earth different from that used in (a). The sealing solution on the coating after permeation is then baked.

TECHNOLOGICAL FIELD

The present invention relates to a manufacturing method for material foruse in molten metal baths, such as rollers or the like, which areinstalled in molten metal baths in continuous molten metal plating linesfor thin steel plates employed in the manufacture of automobiles,household electronic appliances, office equipment, constructionmaterials, and the like, and relates to a manufacturing method formaterials for use in molten metal baths having flame coatings which havesuperior corrosion resistance with respect to molten zinc plating baths,molten aluminum plating baths, and molten zinc-aluminum plating baths.The materials for use in molten metal baths manufactured by means of thepresent invention include not merely the rollers or various memberswhich are immersed in the plating bath, but also members for metalplating accessory facilities onto which molten metal is splattered.

BACKGROUND ART

Conventionally, as rollers which were employed in continuous molten zincplating baths, continuous molten aluminum plating baths, or continuousmolten zinc-aluminum plating baths, as well as members of molten platingaccessory facilities onto which these molten metals are splattered,rollers made of heat-resistant steel, the surface of which is coatedwith various types of cermet system materials or oxide system ceramicmaterials, and which is then subjected to sealing treatment using achromic acid system solution, a metal alkoxide alcohol solution, acolloidal silica solution, or the like, are employed, and have had somesuccess.

However, when members are employed in which various types of cermetmaterials or oxide system ceramic materials are flame-coated onto thesurface of a roller in a molten metal plating bath, and thenconventional sealing treatment is carried out, when such members areemployed in molten metal baths for a long period of time, there isintrusion of molten metal into the flame coating as a result of adecline in the corrosion resistance with respect to molten metal ofsealing treatment itself, or there is intrusion of molten metal into theholes present in the flame coating, and thereby, erosion or alloying ofthe material parts of the members for use in molten metal baths occurs,and this is a cause of peeling of the flame coating.

Furthermore, when rollers for use in molten metal plating baths areemployed which have sealing treatment executed by conventionalflame-sprayed surface coatings, as a result of contact with the passingplate material (steel plate), the flame coating on the surface of theroller in the bath, which was subjected to sealing treatment, is likelyto be abraded, so that the sealing effect decreases, and thereby,intrusion of the molten metal into the flame coating occurs, and this isalso a cause of the peeling of the flame coating as described above.

It has been proposed, in Japanese Patent Application No HEI 9-122904,that as a means for solving this problem, an oxide ceramic flame coatingin which a variety of oxides are combined be formed after flame coatinga cermet material, comprising metal borides within a range of 5-60weight percent, one or more of Co, Cr, Mo, or W in an amount within arange of 5-30 weight percent, the remainder comprising metal carbidesand unavoidable impurities, onto the surface of a steel member, andconducting sealing treatment using an inorganic sealing agent on thiscomposite coating. An example of the inorganic system sealing agentdescribed here is a colloidal silica solution. With respect to thiscolloidal silica solution, in general, this is a solution comprisingonly a colloid of ultrafine granules of silicic acid having a graindiameter within a range of 1-100 nanometers. By means of this, there isa sealing effect; however, it is not sufficient, and concrete measuresfor improving the properties thereof have been desired.

The present invention solves the problems described above in theconventional technology; it has as an object thereof to provide amanufacturing method for members for use in molten metal baths, whichhave flame coatings having superior resistance to corrosion andresistance to peeling with respect to molten metal.

DISCLOSURE OF THE INVENTION

As a result of diligent study by the present inventors in order toattain the object described above, it was learned that a flame coatingfor sealing by using a solution which contains inorganic binder at aweight ratio within a range of 0.3-3.0 with respect to a weight of 1.0of inorganic colloid in an inorganic colloid compound solutioncontaining 5-50 weight percent of an inorganic colloid having a graindiameter within a range of 5-50 nanometers, has superior corrosionresistance and resistance to peeling with respect to molten metal, andthus the present invention has been made.

In the present invention, which is based on the discovery describedabove, a fundamental principle is a manufacturing method for membersused in molten metal baths having a coating which has superior moltenmetal corrosion resistance, wherein, with respect to a cermet flamecoating formed on the outermost surface of a substrate, or with respectto the coating formed by oxide system ceramics formed on the outermostsurface of a substrate (including a coating formed by an oxide systemceramic formed on a cermet flame coating formed on the surface of asubstrate), when the coating forms the uppermost coating layer of theproduct, a solution in which an inorganic binder is mixed at a weightratio within a range of 0.3-3.0 with respect to a weight of 1.0 of aninorganic colloid present in an inorganic colloid compound solution, inan inorganic colloid compound solution containing 5-50 weight percent ofan inorganic colloid having a grain diameter within a range of 5-50nanometers, is applied or sprayed as a sealing solution and is allowedto permeate, and is then baked to carry out sealing treatment.

Furthermore, it is also a fundamental principle in the present inventionthat the inorganic colloid compound solution contains one or more ofSiO₂, Al₂O₃, TiO₂, and ZrO₂, having a grain diameter within a range of5-50 nanometers, and that the cermet flame coating formed on the surfaceof the substrate contains metal borides within a range of 5-60 weightpercent, and contains one or more of Co, Cr, Mo, and W in an amountwithin a range of 5-30 weight percent, the remainder comprising metalcarbides and unavoidable impurities.

Furthermore, in the present invention, it is a fundamental principlethat phosphate systems or silicate systems be used as the inorganicbinder, and that the uppermost layer of the roller barrel employs acermet flame coating or a ceramic flame coating comprising oxides.

Additionally, the present invention includes, in the fundamentalprinciples thereof, application to those in which a) the oxide systemceramic flame coating formed on the outermost surface of the substratecomprises an oxide containing 5% or more of a compound oxide comprisingone or more of Al, Ti, V, Cr, Fe, Co, Rh, In, and rare earths (Sc, Y,and lanthanides) which are trivalent metal elements, and b) one or morerare earths (Sc, Y, and lanthanides) differing from a).

The structure and function of the present invention will now beexplained.

In the cermet flame coating or oxide system ceramic flame coating whichis produced on the surface of rollers or members immersed in the moltenmetal plating bath or molten plating accessory equipment onto whichmolten metal is splattered, the molten metal intrudes into the holesremaining within the coating, and this is a cause of peeling of theflame coating.

In the cermet flame coating or oxide system ceramic flame coating, it isnecessary to fill the holes remaining within the flame coating layerwith a sealing treatment component, and furthermore, it is necessary toprovide corrosion resistance with respect to molten metal, so that, inthe present invention, an inorganic colloid compound solution having aninorganic colloid as the main component thereof is selected as thesealing agent.

Japanese Patent No. 2553937 discloses the formation of a cernet flamecoating formed in the outermost surface of the substrate and comprising5-60 weight percent of metal borides, and 5-30 weight percent of one ormore of Co, Cr, Mo, and W, the remainder comprising metal carbides andunavoidable impurities, an oxide system ceramic flame coating, or aflame coating comprising an oxide system ceramic on top of the cermetflame coating described above formed on the surface of the substrate.Japanese Patent Publication Number HEI 5-209259, and Japanese PatentApplication No. HEI 9-122904 disclose the effects of a cermet flamecoating containing metal borides and an oxide system ceramic flamecoating, and the effects of a flame coating consisting of the formationof an oxide system ceramic on a cermet flame coating which is formed ona substrate surface. Furthermore, the flame coating which is disclosedin “Flame Coating Material and Member Having Coating Formed by the FlameCoating Thereof” (identification number: P98NH122), which was filed onSep. 10, 1998, exhibits characteristics superior to those before.Additionally, with respect to these flame coatings, by executing sealingtreatment in accordance with the present invention, it is possible togreatly increase the effects of molten metal corrosion resistance.

Inorganic colloid employed in the present invention is used as aninorganic colloid compound solution having a grain size within a rangeof 5-50 nanometers. This is necessary in order to fill the holesremaining in the cermet flame coating or the oxide system ceramic flamecoating, so that when the grain size is in excess of 50 nanometers, itis difficult for the granules to intrude from the surface of the flamecoating, and the granules do not fill the holes remaining in thecoating.

With respect to the organic colloid, organic colloidal compound having,in particular, Sio₂, Al₂O₃, TiO₂, and ZrO₂ as chief components thereofare selected. These compounds are selected because (1) they have goodcorrosion resistance with respect to molten metals, and (2) they arechemically stable substances.

As the sealing solution employed in the present invention a liquidsolution which ultimately generates metal oxides is preferable from thepoint of view of permeation. It is an aqueous solution having water asthe chief component thereof, pH of which is set to a range of 7-11 inorder to stabilize the inorganic colloid compound solution.

By allowing the sealing liquid to penetrate the flame coating and thenbaking this, the aqueous component of the sealing liquid whichpenetrates into the spaces in the coating is evaporated, and ceramiccomponents such as metal oxides and the like are formed in the coatingand remain in a sealing state. The baking may be conducted at 450° C.and for a period of 30 minutes, and where necessary, a plurality ofimmersions in the same or different sealing liquids, and baking, may beconducted.

When, after the sealing treatment, the amount of one or more of SiO₂,Al₂O₃, TiO₂, and ZrO₂ generated within the flame coating layer is small,then it is difficult to fill all holes present within the flame coatinglayer, and the holes which are created as a result of the gas componentor the water component which is released during heating after theimmersion remain as holes which are not filled because the amountcontained is small. Thus, the intrusion of the molten metal into theseholes which remain becomes prominent, the substrate is corroded, and theflame coating is likely to peel.

Accordingly, it is necessary to use a solution having an amountcontaining 5% or greater, and in cases where the amount contained is inexcess of 50%, the inorganic colloid compound solution becomeschemically unstable, and SiO₂, Al₂O₃, TiO₂, and ZrO₂ form large granuleswithin the solution in the colloidal state. Accordingly, a solution isemployed which has an amount contained not in excess of 50 weightpercent.

By mixing silicic acid soda or aluminum phosphate or the like as aninorganic binder in the inorganic colloid compound solution, thecolloidal particles such as SiO₂ and the like which are generated withinthe flame coated layer and at the surface of the flame coated layercohere, and furthermore, the intergranular binding forces of thegranules are further increased and they solidify, and the intrusion ofthe molten metal is prevented, so that the corrosion resistance withrespect to molten metal is further increased.

In this case, with respect to the mixing proportions of the inorganiccolloid compound solution and the inorganic binder which is a phosphatesystem or a silicate system, when the weight ratio of the inorganicbinder is less than 0.3 with respect to a weight of 1.0 of the inorganiccolloid within the inorganic colloid compound solution, thestrengthening and improvement effects are not observed, while when thisweight ratio is in excess of 3.0, the microgranules within the colloidalsolution form large granules, and this is undesirable.

BEST MODE FOR CARRYING OUT THE INVENTION

The method of the present invention will be explained by an embodimentin which it is applied to a bath roller for a molten zinc-0.1% aluminumplating line which is chiefly employed in a steel manufacturing line;however, the present invention is not limited thereby.

Embodiment

For the purposes of testing, after an SUS316L steel substrate having adiameter of 30 mmφ and a length of 300 mm was blast-treated with aluminasand, test pieces were used which had the various flame coating andsealing treatments shown in tables 1, 2, and 3 executed thereon. Thethickness of the uppermost layer flame coating was 60 micrometers, andwhere a bond coat was formed, the thickness thereof was 40 micrometers.

With respect to the evaluation method, the test pieces were immersed ina molten zinc-0.1% aluminum bath at a temperature of 450° C., and at5-day intervals, these were removed from the bath temporarily, and werereimmersed, and remained immersed until the total days of immersionbecame 60. An observation was made each time as to whether the flamecoating had peeled or not, and the peeling state of the flame coatingwas thus assessed. The results of the testing are shown in Table 1.

TABLE 1 Sealing Treatment Molten Metal Bath Grain Corrosion Solu- Dia-Bind- Resistance Test Classi- Num- tion meter er 10 30 60 fication ber(X) (nm) (Y) X:Y days days days Embodi- 1 A 10-30 a 1:1 Θ Θ ◯ ments of 2A 5-50 a 1:0.5 Θ Θ ◯ the Pre- 3 A 5-50 a 1:1 Θ Θ ◯ sent In- 4 A 5-50 a1:2 Θ Θ ◯ vention 5 A 10-50 b 1:1 Θ Θ ◯ 6 A 10-50 c 1:1 Θ Θ ◯ 7 A 10-50d 1:1 Θ Θ ◯ 8 13 10-50 a 1:1 Θ Θ ◯ 9 A 50-100 a 1:1 Θ Δ X Compara- 10None ◯ Δ X tive 11 Chromic acid solution Θ ◯ x Examples 12 SiO₂-systemsol-gel Θ A X solution (alkoxide solution) Embodi- 13 A 10-50 a 1:1 Θ ΘΘ ments of 14 A 10-50 b 1:1 Θ Θ Θ the Pre- 15 A 10-50 d 1:1 Θ Θ Θ sentIn- 16 B 10-50 a 1:1 Θ Θ Θ vention 17 C 10-50 a 1:1 Θ Θ Θ 18 D 10-50 a1:1 Θ Θ Θ 19 E 10-50 a 1:1 Θ Θ Θ 20 F 10-50 a 1:1 Θ Θ Θ Compara- 21 NoneΘ ◯ Δ tive 22 Chromic acid solution Θ Θ ◯ Examples 23 SiO₂2-systemsol-gel ◯ A solution (alkoxide solution) Note 1: Uppermost layer flamecoating layer Number 1-12: WC—50% WB—10% CO Number 13-23: Cr₂O₃ + 10%YCrO₃ (Numbers 13-15 and numbers 18-20 have a bond coat [WC—50% WB—10%Co]) Note 2: Leaking test. After immersion in a 450° C. molten zincbath, extraction and comparison. Θ: no zinc adhering ◯: partialdeposition of zinc; however, it is easily removed A: partial peeling ofthe coating or partial deposition of zinc which can not be easilyremoved X: deposition of zinc over entire surface or widespread peelingof the coating Note 3: X:Y Mixing weight ratio (X: inorganic colloidcomponent, Y: inorganic binder)

TABLE 2 Type of Inorganic Chemical Solution Colloidal ComponentContaining Oxides (%) Component (%) Solution SiO₂ Al₂O₃ TiO₂ ZrO₂ Na₂OHNO₃ H₂O Solution A  5  5 — — 0.5 — Remainder Solution B 30 — — — 0.5 —Remainder Solution C 30  5  5 — 0.5 — Remainder Solution D — 30  5   5 —2 Remainder Solution E — — 20 20 — 2 Remainder Solution F — 10 — 30 — 2Remainder Note: The values indicate weight %.

TABLE 3 Type of Inorganic Binder Solution Components (weight %) SolutionP₂O₅ Al₂O₃ Na₂O SiO₂ K₂O H₂O a 32 8 Remainder (aluminum phosphatesystem) b (sodium 28 12 Remainder phosphate system) c (sodium 10 30Remainder silicate system) d 30 20 Remainder (potassium silicate system)

In Table 1, numbers 1-8 and numbers 13-20 are embodiments of the presentinvention, while numbers 9 through 12 and numbers 21-23 are comparativeexamples.

In the embodiments of numbers 1-8 and numbers 13-20 (in numbers 13-15and number 18-20, a flame coating having a thickness of 40 micrometersand comprising WC-50% WB-10% Co was formed as a bond coat), the varioussealing treatments of the present invention were conducted with respectto those having the typical cermet materials, which are actuallyemployed as materials for molten metal baths in actual baths in moltenzinc plating lines, or having metal oxide system ceramic materials, ascoatings which are flame-coated layers on the uppermost layer.

In addition, numbers 10-12 and numbers 21-23 are comparative exampleswhich employ the conventional sealing treatments on the flame-coatedlayers described above, and number 9 is a comparative example whichconducts a sealing treatment with a sealing agent in which the inorganiccolloid granules are outside the predetermined ranges.

It can be understood from Table 1 that the members for use in moltenmetal baths produced by means of the present invention, in comparisonwith members using the conventional sealing techniques, have no peelingof the flame coating in a molten zinc-0.1% aluminum bath immersion, andpossess superior corrosion resistance with respect to molten metalbaths. In the present embodiment, the results were applied to a moltenzinc-0.1% aluminum plating bath; however, similar effects are obtainablein other embodiments in which application is to a molten aluminumplating bath or a molten zinc-50% aluminum plating bath, so that theeffects of the present invention are confirmed.

Industrial Applicability

The composition of the present invention is as described above, so thatit is possible to provide a manufacturing method for members for use inmolten metal baths, which forms a sealed flame coating having superiorcorrosion resistance with respect to molten zinc baths or moltenzinc-aluminum baths and superior resistance to peeling, and it becomespossible to operate a plating line continuously for a long period oftime, and this is extremely useful in manufacturing.

What is claimed is:
 1. A manufacturing method for a member with acoating having molten metal corrosion resistance for use in a moltenmetal bath, comprising: applying, on a coating formed of oxide systemceramics formed on an outermost surface of a substrate, a sealingsolution including an inorganic colloid compound solution containing aninorganic colloid having a grain diameter within a range of 5-50nanometers in an amount of 5-50 weight percent, and an inorganic binder,said inorganic binder being mixed at a weight ratio of 0.3-3.0 withrespect to a weight of 1.0 of the inorganic colloid, said oxide systemceramics formed on the outermost surface of the substrate being an oxidecontaining 5% or more of a composite oxide comprising (a) at least oneof Al, Ti, V, Cr, Fe, Co, Rh, In and rare earths, which are trivalentmetal elements, and (b) at least one rare earth different from that usedin (a), and baking the sealing solution on the coating after permeation.2. A manufacturing method according to claim 1, wherein said oxidesystem ceramics formed on the outermost surface of the substrate arecoated on a cermet flame coating on the substrate.
 3. A manufacturingmethod according to claim 2, wherein said rare earths used in (a) and(b) comprise Sc, Y or lanthanides.
 4. A manufacturing method accordingto claim 1, wherein said inorganic colloid contained in the inorganiccolloid compound solution is at least one member selected from the groupconsisting of SiO₂, Al₂O₃, TiO₂, and ZrO₂.
 5. A manufacturing methodaccording to claim 1, wherein phosphate systems or silicate systems areemployed as the inorganic binder.
 6. A manufacturing method according toclaim 1, wherein the member is a roller barrel, and a cermet flamecoating or ceramic flame coating comprising oxides as the coating formedof oxide system ceramics is formed on the uppermost layer of the rollerbarrel.